The composition and role of the microbiota of oral mucous membranes in both health and lesions of the soft tissues are not well understood. Preliminary data from systemically healthy subjects show that significant differences exist in bacterial composition on different mucous membranes within the same subject. This suggests that different surfaces represent different habitats that favor colonization by different microorganisms. Early indications also suggest differences between the microbiotas of soft tissues in periodontally healthy and periodontally diseased subjects. It is likely that pathologic changes in the oral mucous membranes will favor colonization by different organisms than those found on healthy soft tissue. This study proposes to comprehensively examine the microbiota of different oral mucous membranes in health and disease using checkerboard DNA-DNA hybridization. Specific Aims are 1. To compare the microbial composition of samples from 8 different oral mucous membrane sites with that found in saliva, supra and sub-gingival plaque in subjects stratified according to periodontal status (health or disease) and smoking status (current or never). 2. To compare the microbiota found in oral cancer lesions with that found on healthy soft tissues in the same subjects and systemically healthy subjects. 3. To examine changes in the mucous membrane microbiota during and after a standard protocol of chemotherapy and radiation therapy. Subjects will be followed for five years. A cross-sectional study of four groups of 25 systematically healthy subjects will be done at Forsyth Dental Center. Subjects will be selected based on smoking history and periodontal disease status. Samples will be taken from the dorsum, lateral and ventral surfaces of the tongue, floor of mouth, cheek, hard palate, vestibule/lip, attached gingiva and saliva as well as supra and subgingival plaque of the mesial aspect of each tooth in each subject. Each sample will be tested for its content of 40 bacterial species using checkerboard DNA-DNA hybridization. Comparisons will be made for each species among sample location, disease status and smoking history. A longitudinal study of 50 oral cancer patients is proposed of the Dana Farber Cancer Institute. Samples from the cancer lesion, the mucosal surfaces, saliva, supra and subgingival plaque will be taken and evaluate for their content of 40 bacterial species at baseline, during and after a standard protocol of combined-chemotherapy and radiation therapy. Comparisons will be made at baseline between microbial species on cancer lesions and healthy surfaces. Mucositis will be scored and salivary function tested. Cultural techniques, PCR and cloning will also be used to seek organisms that were not in the standard battery of probes. The data from the proposed studies should help to clarify the ecological relationships between oral bacterial species and the habitats that they colonize. In addition, the studies should indicate if the microbiota on cancerous lesions differs from that on healthy mucous membranes. Detection on unusual microbial shifts in mucositis might suggest possible routes to minimizing this condition.